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Date:   Tue, 30 Aug 2022 14:00:02 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     =?iso-8859-1?Q?Martin-=C9ric?= Racine <martin-eric.racine@iki.fi>
Cc:     Ben Hutchings <ben@decadent.org.uk>, x86@kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        1017425@bugs.debian.org, stable@vger.kernel.org,
        regressions@lists.linux.dev,
        Daniel Sneddon <daniel.sneddon@linux.intel.com>,
        Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Subject: Re: [PATCH] x86/speculation: Avoid LFENCE in FILL_RETURN_BUFFER on
 CPUs that lack it
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On Tue, Aug 30, 2022 at 02:42:04PM +0300, Martin-?ric Racine wrote:
> Greetings,
> 
> On Fri, Aug 19, 2022 at 3:15 PM Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > On Fri, Aug 19, 2022 at 01:38:27PM +0200, Ben Hutchings wrote:
> >
> > > So that puts the whole __FILL_RETURN_BUFFER inside an alternative, and
> > > we can't have nested alternatives.  That's unfortunate.
> >
> > Well, both alternatives end with the LFENCE instruction, so I could pull
> > it out and do two consequtive ALTs, but unrolling the loop for i386 is
> > a better solution in that the sequence, while larger, removes the need
> > for the LFENCE.
> 
> Have we reached a definitive conclusion on to how to fix this?

https://git.kernel.org/tip/332924973725e8cdcc783c175f68cf7e162cb9e5